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What is fragile X syndrome?

  • Fragile X Syndrome is a genetic condition. It is inherited on the X chromosome.
  • It is the most common known cause of inherited intellectual disability.
  • Fragile X syndrome affects about 1 in 3600 males and 1 in 4000 females and about 1 in 150 females and 1 in 800 males are carriers of the condition.

Clinical features

Individuals with fragile X syndrome have a normal life expectancy.
Males with fragile X syndrome are usually more affected than females.
Some of the typical features found in males with fragile X syndrome are described below. These features may not always be present and may vary in severity between individuals.

Females with fragile X syndrome

  • Females are usually not as affected as males.
  • Around half will have intellectual disability.
  • Many will have learning problems and emotional and behavioural problems such as shyness, social anxiety or mood disorders.
  • Typical features include difficulty with maths and social anxiety.


Fragile X is diagnosed by a genetic (DNA) test. This test can also be used to identify people who are carriers of fragile X syndrome. (See Genetic carrier testing) Genetic counselling is available to provide information and support.


There is no cure for fragile X syndrome but specific treatment strategies and methods of teaching are available that can help people affected by fragile X syndrome. Because the impact of fragile X is so varied, treatment plans need to be specifically targeted at each persons individual needs. (See Management)

Developmental disability

  • Intellectual disability – this occurs in all males with fragile X syndrome
  • Learning disability
  • Speech delay or minimal speech
  • Fine and gross motor delay
  • Coordination difficulties
  • Poor muscle tone (also called hypotonia)

Behavioural and emotional problems

  • Anxiety
  • Hyperarousal
  • Attention deficit hyperactivity disorder
  • Speech disturbances
    • Variable volume and pitch
    • Repetitive patterns in speech and behaviour
    • Rapid speech with repetition and off topic remarks (also called cluttering)
  • Autistic like features
    • Hand-flapping
    • Biting
    • Poor eye contact
    • Socially inappropriate interactions
    • Mimicry
    • Preoccupation with objects
  • Sensory defensiveness
    • Gaze aversion
    • Aversion to touch, loud noises, bright lights and strong smells
  • Mood instability such as aggressive outbursts or depression

Medical conditions

  • Up to 20% have epilepsy
  • Recurrent middle ear infections (otitis media)
  • Eye problems such as squint – also called strabismus
  • Heart valve problems

Physical characteristics

Physical characteristics may not always be present – especially before puberty

  • Large prominent ears
  • High broad forehead
  • High arched palate
  • Large testicles
  • Problems with connective tissue eg flat feet or hyper elastic skin or loose joints